There's completely no difference [with ridges] imo. I've tried the WRM, and they don't really change anything when it comes to slices(although that kinda makes sense cause they're on the outside anyway). And as far as preventing slipping your hands off the cube, it's really rare anyway so the ridges again don't really change anything. Basically this is the story of ridges:
Moyu: "Let's put ridges!"
Cubers before trying: "WTH ARE U CRAZY THIS CUBE SUX"
Cubers after trying: "Oh. This is basically the same as a normal cube. Whatever I guess"
Moyu: "OK FINE WELL REMOVE RIDGES"
Cubers before trying: "Um, we didn't really have an opinion on the ridges anyway, so whatever I guess"
Cubers after trying: "Yeah this is literally the same cube except the LM version with slightly different ascetics"
Moyu: "OK FINE WELL JUST MAKE A WRM WITH RIDGES"
Cubers: "Holy crap we don't even want these just make a GTS4 already"